1. Technical Field
The present disclosure relates to a workpiece conveying apparatus for conveying multiple workpieces such as chip electronic components. More specifically, the present disclosure relates to a workpiece conveying apparatus and an electronic-component conveying apparatus of the type that conveys workpieces by moving a conveying table, which has through holes serving as container portions for containing workpieces, over a conveying stage.
2. Background Art
Conventionally, in manufacturing chip electronic components, after chip electronic components are fabricated and inspected for their properties, selection of non-defective components and defective components according to their properties is performed. The chip electronic components are also classified into a plurality of groups according to their properties. To automate these operations and increase productivity, various manufacturing apparatuses have been proposed.
For example, Patent Document 1, which will be specified below, discloses an exemplary electronic-component conveying apparatus of this type. In the electronic-component conveying apparatus, a disk-shaped conveying table is arranged such that it contacts a conveying surface of a table base to convey electronic components. The disk-shaped conveying table is connected to a rotary drive source and is capable of rotation about the central axis thereof. The conveying table has a plurality of through holes along the circumference thereof, each of which can contain one of the electronic components successively supplied from a hopper. The hopper supplies electronic components into these through holes. The electronic components are conveyed in the circumferential direction of the conveying table by the conveying table sliding and rotating on the conveying surface of the table base.
In this apparatus, while the electronic components are conveyed in the circumferential direction of the conveying table, the properties of the electronic components are measured. Then, the electronic components having gone through the property measurement are dismounted from the through holes by any suitable means for dismounting the electronic components, which are then subjected to selection of non-defective components and defective components according to the result of the measurement, or classification according to the properties.
The conveying surface has vacuum recesses communicating with the through holes and connected to a vacuum suction source or the like, which serves to maintain positions of the electronic components during the conveyance.
FIG. 10 shows a known structure that is used to dismount the electronic components having gone through the property measurement. That is, as shown in FIG. 10, in an electronic-component conveying apparatus 101, the conveying table 102 has through holes 102a. Each through hole 102a contains an electronic component 104. One surface 102b of the conveying table 102 contacts a conveying surface 103a of a table base 103.
The table base 103 has exhaust holes 103b, which open in the conveying surface 103a at positions where the electronic components 104 are to be dismounted. The exhaust holes 103b extend from the conveying surface 103a to a surface 103c opposite the conveying surface 103a and are connected to a compressed-air supplying hose 105. The compressed-air supplying hose 105 is connected to a compressed-air supplying source, such as a compressor or a cylinder.
When the conveying table 102 is rotated and the electronic components 104 after the measurement are brought to the electronic-component dismounting position, the exhaust holes 103b, which have a smaller diameter than the opening of the through holes 102a, face a part of the through holes 102a. Then, compressed air is jetted through the exhaust holes 103b. The pressure of the compressed air causes the electronic components 104 to move to the outside of the through holes 102a, whereby the electronic components 104 are dismounted.
This method allows the electronic components 104 to be dismounted without receiving mechanical impact, and thus, the electronic components 104 are negligibly damaged.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-226101
As described above, the conveying table 102 slides and moves on the conveying surface 103a of the table base 103 independently of the table base 103. Therefore, after the electronic components 104 are dismounted by compressed air, the conveying table 102 is further rotated. As a result, the exhaust holes 103b are closed by the one surface 102b of the conveying table 102 again.
In this case, there will be no problems if the compressed air is completely discharged into the through hole 102a to cause the electronic components 104 to be dismounted, and the exhaust holes 103b are then closed by the one surface 102b of the conveying table 102 after supply of compressed air is stopped.
However, with an increased conveying speed, the openings of the exhaust holes 103b are sometimes closed by the conveying table 102 while compressed air remains in the exhaust holes 103b. In such cases, compressed air remains in the exhaust holes 103b and generates residual pressure.
Thus, when the conveying table 102 is further rotated and subsequent through holes containing electronic components not to be dismounted at the electronic-component dismounting position are brought to positions above the exhaust holes 103b, the electronic components not to be dismounted are sometimes dismounted because of the residual pressure. Thus, in the conventional electronic-component conveying apparatus, the conveying table 102 is not rotated or moved immediately after the electronic components 104 are dismounted, and the conveying table 102 needs to wait for a predetermined time so that the air is completely discharged. That is, a waiting time to release residual pressure is required, which prevents the electronic-component conveying apparatus from operating at a high speed.
In particular, as the size of the electronic components becomes small, the size of the exhaust holes 103b also needs to be small. If the size of the exhaust holes 103b is small, the amount of air jetted therethrough becomes insufficient. Therefore, the length of the waiting time to remove residual pressure needs to be further increased. There is a problem in that, however, even if the length of the waiting time is increased, residual pressure cannot be sufficiently released.